Semiconductor device with memory controller that controls page mode access

ABSTRACT

A memory controller and data processor have their operation mode switched from the page-on mode for high-speed access to a same page to the page-off mode in response to consecutive events of access to different pages, so that the memory access is performed at a high speed and low power consumption.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/931,860filed Aug. 20, 2001, now U.S. Pat. No. 6,587,934.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a memory controller which can havememory access, a data processor which has the memory controller and acentral processing unit, and a data processing system which has the dataprocessor and a memory. The invention also relates to a technique whichis useful when applied to a semiconductor device having theabove-mentioned items formed in one package.

2. Description of the Prior Art

A data processor having a central processing unit (CPU) makes access tomemories which include a main memory and a cache memory. The main memorystores programs to be run and data to be processed by the CPU. The mainmemory formed in a semiconductor device is known to be a large-capacitymemory which is typically made of volatile memories such as a DRAM(dynamic random access memory) or nonvolatile memories such as a flashmemory. The cache memory is made of memories having relatively smallcapacities such as a SRAM (static random access memory). The cachememory is located between the CPU having a high-speed operation and themain memory which operates slower than the CPU, thereby absorbingdifference in their operational speeds.

For a high-speed operation of a data processing system having a CPU,cache memory and main memory, there has been a technique of using thesense amplifiers of the DRAM of main memory in a manner like cachememory. The technique of using DRAM's sense amplifiers in a manner likecache memory will be explained as follows. The data processor first putsout a row address to the DRAM. The DRAM has its word lines selected by arow address, and data of the full one line on the selected word line aretransferred to and held by the sense amplifiers. The data processor nextputs out a column address to the DRAM. The column address selectscertain column switches, causing the sense amplifiers to release thedata.

The sense amplifiers hold the data of the full one line of the selectedword line continuously after the readout of data. At the next DRAMaccess by the data processor, if the row address is the same as theprevious one, the data processor puts out only a column address.Generally, word line selection takes a relatively long time, whereas byretaining data in the sense amplifiers, it is possible to read out datain a short time for an event of access with the same word line, i.e.,access to the same page.

However, the foregoing prior art involves the following problem. In casedata is to be read out from a word line which is different from the wordline where data are held by sense amplifiers, i.e., at the occurrence ofcache error in the cache-wise use of sense amplifiers, it is necessaryto cancel the selection of the immediate word line, precharge the datalines, and thereafter select a new word line. The need of precharging atthis access results in a longer data read time than usual data readout.

There are several techniques intended to overcome the above-mentionedproblem as described in JP-A Nos. 1994-131867, 1995-78106 and2000-21160.

The JP-A No. 1994-131867 discloses a technique for speeding up the readand write operations of a DRAM, with its sense amplifiers being used ascache memory, even at the occurrence of cache error. Specifically, theDRAM has its data lines divided into data lines which are connected tothe memory cells and pre-amplifiers, and global data lines which areconnected to the main amplifiers used as cache memory.

It also shows the arrangement of a means of shorting the data lines,which are connected with the memory cells and pre-amplifiers,independently of the global bit lines. This arrangement enables theprecharging of the data lines which are connected with memory cells andpre-amplifiers even in the data holding state for one page of the mainamplifiers connected to the global data lines, and thus enables thepreparation for reading out data from another page, i.e., another wordline.

The JP-A No. 1995-78106 discloses a technique for speeding up the readand write operations of a DRAM, with its sense amplifiers for memorybanks being used as cache memory, even at the occurrence of alternateaccess between memory banks. Specifically, a data processing system isprovided in its DRAM control circuit with row address memory means incorrespondence to the memory banks. This arrangement enables thejudgement as to whether the memory access is to the same row address asthe previous access, i.e., whether the access is to the same page, foreach memory bank, and thus enables the high-speed block data transfer.

The JP-A No. 2000-21160 discloses a technique for the use of senseamplifiers for memory banks of a multi-bank DRAM as cache memory. Itshows, with the intention of enhancing the hit rate of sense amplifiercache, a means of advanced reading of data of a predicted address basedon the advanced issuance of the next address which is determined byadding a certain offset value to the previous address of the memory bankwhich has been accessed previously.

The inventors of the present invention have found the unevenness ofaccess to the main memory in reading a program to be run by the centralprocessing unit or reading data out of the main memory. For example,there are a case of frequent access to the same page (same word line) ofthe main memory, a case of frequent access to different pages, and acase of access to a same page and access to different pages at an equalfrequency. The unevenness of access results largely from thecharacteristic of a program. The inventors of the present invention havefound that the above-mentioned prior arts cannot deal with theunevenness of access frequency sufficiently and cannot solve the problemof slower data read/write operations from/to the main memory due to theunevenness.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a data processor havingits main memory sense amplifiers, e.g., DRAM, used as cache memory, anda data processing system having the data processor and main memory, withthe intention being the speed-up of main memory access thereby to speedup the whole data processing system.

These and other objects and novel features of the present invention willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings.

Representing means of carrying out the present invention are as follows.

There is provided a means of checking as to whether the immediate memoryaccess is to the same page as of the previous access or to a differentpage, and switching the memory control mode accordingly. There isprovided a memory controller having a page mode, wherein the page modeis cancelled at an event of different page access or the row addressoutput is skipped at an event of same page access. Upon canceling thepage mode, it enters the operation mode of precharge control afterputting out a column address at an event of memory access.

The precharge control is to bring the RAS signal to the high level onexpiration of a certain time length following the output of a columnaddress. In other words, the precharge control is to issue a prechargecommand on expiration of a certain time length following the output ofthe column address.

The memory controller may have a register for setting as to whether ornot the cancellation of page mode is to take place. The page mode willalso be called “page-on mode” or “RAS-down mode”.

Another means is a memory controller having a page mode, wherein thepage mode is cancelled at successive events of access to differentpages. At an event of different page access, it implements prechargecontrol and thereafter puts out a row address, or it implements theprecharge control without the row address output at an event of samepage access.

The precharge control is to put out a high-level RAS signal. Inaddition, the precharge control is to issue a precharge command, and putout a row address on expiration of a certain time length following theissuance of the precharge command.

Upon canceling the page mode, the memory controller enters the operationmode of bringing the RAS signal to the high level on expiration of acertain time length following the column address output at an event ofmemory access. In addition, upon canceling the page mode, it enters theoperation mode of issuing the precharge command on expiration of acertain time length following the column address output at an event ofmemory access.

The memory controller may have a register for setting as to whether ornot the cancellation of page mode is to take place.

Another means is a memory controller having a first operation mode andsecond operation mode, and it switches from the first mode to the secondmode at an event of access to a second page which is different from afirst page, following the access to the first page. In the second mode,it switches from the second mode to the first mode at an event of accessto a third page following the access to the third page. The first modeis to have successive events of access to a same page, and the secondmode is to have successive events of access to different pages. The timeexpended to make access to a same page a certain number of times in thefirst mode is shorter than the time expended to make access to the samepage the same number of times in the second mode.

Another means is a memory controller having a first operation mode inwhich memory access takes place with the output of a column address andwithout the output of a row address, and a second operation mode inwhich memory access takes place with the implementation of prechargecontrol following the output of a row address and column address. Itswitches to the first mode at an event of memory access with the outputof a row address and column address following the implementation ofprecharge control. At an event of memory access to a same row address inthe second mode, it switches to the first mode.

The memory controller may have a register for setting as to whether ornot the switching between the first and second modes is to take place.

The precharge control of the second mode is to put out a high-level RASsignal on expiration of a prescribed time length following the columnaddress output. In addition, the precharge control of the second mode isto issue the precharge command on expiration of a prescribed time lengthfollowing the column address output.

Another means is a data processing system including a central processingunit (CPU) which puts out an address, a memory controller which issupplied with the address and adapted to operate in a first mode andsecond mode, and a memory which is controlled by the memory controller.In the first mode, the memory controller switches from the first mode tothe second mode at an event of access to a second page which isdifferent form a first page following the access to the first page.

The data processing system has a register circuit for setting as towhether or not the switching between the first and second modes is totake place. The CPU can alter the setting of the register circuit. TheCPU and memory controller may be formed on a same semiconductor chip.Alternatively, the CPU, memory controller memory may be formed in onesemiconductor package.

Another means is a memory controller having a first memory access modein which it makes access to the memory by putting out a column addressbut without putting out a row address, a second memory access mode inwhich it precharges the memory and thereafter puts out a row address andcolumn address, and a third memory access mode in which it puts out arow address and column address to the memory and thereafter prechargesthe memory, and operating to have the first memory access, andthereafter the second memory access, and thereafter the third memoryaccess. Alternatively, the first memory access may be followed by thesecond memory access a number of times, which may be followed by thethird memory access.

Still another means is a memory controller having an input node, a firstregister circuit which holds the address put to the input node, a firstcomparator circuit which compares the address put to the input node withthe address held by the first register circuit, a second comparatorcircuit which compares the output of the first comparator circuit withthe contents of a second register circuit, and a first circuit which isset to a first state or second state depending on the output of thesecond comparator circuit. The first comparator circuit releases a valuewhich is the number of times of the comparison result of inequality ordisagreement between the address held by the first register circuit andthe address put to the input node, and the second comparator circuitcompares the count value provided by the first comparator circuit withthe contents of the second register circuit.

The memory controller may further include a second circuit whichreleases a first and second parts of the address put to the input nodein response to the setting of the first state of the first circuit orthe first part of the address put to the input node in response to thesetting of the second state of the first circuit, and an output nodewhich releases the output of the second circuit to the memory.

Alternatively, the first register circuit holds part of the address putto the input node, and the first comparator circuit compares part of theaddress put to the input node with part of address held by the firstregister circuit. Alternatively, the first comparator circuit compares afirst address put to the input node with a second address which has beenput to the input node before the first address.

Alternatively, an address put to the input node has a number of bits andthe first register circuit has a number of fields, and the firstcomparator circuit compares the first address with the address which isheld in one of the fields specified by a certain bit of the firstaddress. The first and second parts of address may be a row address anda column address, respectively, of the memory. The input node may besupplied with an address which is put out by the CPU.

Another means is a memory controller which can adjust the correspondencebetween an address put out by the CPU and a memory address based oninformation of the line size, index and tag indicative of the structureof the primary cache of CPU and information of the column address, rowaddress and bank address indicative of the structure of the memoryaccessed by the CPU.

In combination with the foregoing means, with the intention of furtherraising the frequency of access to the same page of the memory, an eventof access to a memory is followed by the advanced issuance of the nextaddress (evaluated by the addition of a certain offset value to theprevious address) and data of the predicted address is held in the senseamplifiers of a bank in a different memory.

The memory may be controlled based on the judgement as to whether theprevious predicted address is to the same page as the immediate access,and the predicted address is validated in the case of a same page accessor invalidated in the case of a different page access.

The memory controller may further include an additional arrangement foraligning automatically an address put out by the CPU and a memoryaddress based on information of the line size, index and tag indicativeof the structure of the primary cache of CPU and information of columnaddress, row address and bank address indicative of the structure of thememory accessed by the CPU. This additional arrangement can be eitheradded to the foregoing arrangement or used independently to achieve theeffectiveness of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the data processing system based on a firstembodiment of this invention;

FIG. 2 is a block diagram of the memory module of the first embodiment;

FIG. 3 is a schematic circuit diagram of a memory bank of the firstembodiment;

FIG. 4 is a timing chart showing the operation of the memory controlcircuit of the first embodiment;

FIG. 5 is a block diagram of the memory control circuit of the firstembodiment;

FIG. 6 is a table showing information held by the page access checkingcircuit of the first embodiment;

FIGS. 7A and 7B are timing charts showing the operation of the pageaccess checking circuit of the first embodiment;

FIG. 8 is a flowchart showing the operation of the mode change circuitof the first embodiment;

FIG. 9 is a table showing the operation of the address generationcircuit of the first embodiment;

FIG. 10 is a set of timing charts showing the operation of the memorycontrol circuit of the first embodiment;

FIG. 11 is a timing chart showing the refresh operation of the firstembodiment;

FIGS. 12A, 12B and 12C are diagrams showing the effectiveness of thisinvention;

FIG. 13 is a block diagram of the memory control circuit based on asecond embodiment of this invention;

FIG. 14 is a table showing information held by the predicted addresschecking circuit of the second embodiment;

FIG. 15 is a table showing information held by the predicted addressgeneration circuit of the second embodiment;

FIGS. 16A and 16B are timing charts showing the operation of thepredicted address generation circuit and predicted address checkingcircuit of the second embodiment;

FIG. 17 is a flowchart showing the predicted address generation modechange circuit of the second embodiment;

FIGS. 18A and 18B are timing charts showing the operation of the pageaccess checking circuit and address generation circuit of the secondembodiment;

FIG. 19 is a timing chart showing the operation of the memory controlcircuit of the second embodiment;

FIG. 20 is a block diagram of the memory control circuit based on athird embodiment of this invention;

FIG. 21 is a block diagram of the data processing system based on thethird embodiment of this invention;

FIG. 22 is a diagram showing address alignment conducted by theautomatic address alignment circuit of the third embodiment;

FIG. 23 is a diagram showing address alignment conducted by theautomatic address alignment circuit of the third embodiment;

FIG. 24 is a set of timing charts showing the operation of a fourthembodiment of this invention;

FIG. 25 is a flowchart showing the operation of the mode change circuitof the fourth embodiment;

FIG. 26 is a set of timing charts showing the operation of a fifthembodiment of this invention; and

FIG. 27 is a diagram of a semiconductor device having the inventive dataprocessing system built within a package.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows by block diagram the data processing system based on thefirst embodiment of this invention. A data processor (MS0) includes acentral processing unit (CPU) and a primary cache memory (L1C). The dataprocessor MS0 may further include other devices such as a floating pointunit (FPU), but these devices which are not directly concerned with thepresent invention are not shown and explained.

The CPU uses a 32-bit address signal, although this is not compulsory,to deal with the address space, which is partially allotted to a memorymodule (MEM). The memory module MEM, which has a role of the mainmemory, is made up of a number of memories (ME0-ME7). The memories storeprograms and data to be run and used by the CPU (in the followingexplanation, programs and data will be termed commonly as “data” withoutdistinction). Each memory of this embodiment is made up of four memorybanks each provided with sense amplifiers. The number of memory banksmay be two or eight or more instead of four, or the memory may not evenhave a bank structure.

Provided between the data processor MS0 and memory module MEM is amemory control unit (MCU) which controls the memory module MEM. Thememory control unit is connected with a PCI (peripheral componentinterconnect) bridge circuit (BRG) which is used for data transfer fromthe outside of the data processing system to the memory module.

The memory control unit MCU has a refresh control circuit (RFC) whichcontrols the refreshing of the memories in the memory module. It alsohas an arbiter circuit (ARB) which arbitrates the memory access from theCPU, memory access from the refresh control circuit for the refreshingof memory module, and memory access from the PCI bridge circuit BRG. Thearbiter circuit watches access requests from the CPU, refresh controlcircuit and PCI bridge circuit, and it grants one of access requests inaccordance with the priority order. In this embodiment, the refreshcontrol circuit, CPU and PCI bridge circuit have the first, second andthird priority orders, although this is not compulsory.

The memory control unit further has a memory control circuit (MC) whichcontrols the memory module in response to an access request granted bythe arbiter circuit. The refresh control circuit implements the refreshoperation necessary for a DRAM as memories of the memory module.

The data processor and memory control unit in combination will be calleddata processor device, but the data processor can incorporate the memorycontrol unit of this invention. The data processor of this embodimentoperates in synchronism with a clock signal CLK (not shown). Thesefeatures are common to all embodiments of this invention.

Next, the operation of the data processing system will be explained. TheCPU makes a data read or write access to the memory module MEM byputting out the read command and memory address to the arbiter circuitARB over a CO0 bus and AD0 bus, respectively. The arbiter circuit grantsthe access request from the CPU in accordance with the arbitration rule,and it puts the read command and address to the memory control circuitMC over an IC0 bus and IAD bus, respectively. On receiving the readcommand and address from the arbiter circuit, the memory control circuitcontrols the memories ME0-ME7 in the memory module MEM.

FIG. 2 shows the detailed structure of the memory module MEM. The memorymodule of this embodiment is made up of eight memories ME0-ME7. Thememory ME0 in the memory module has four memory banks (B0-B3), a mainamplifier (MA) and an input/output buffer (IOBUF). The remainingmemories ME1-ME7 are the same as ME0. The memory bank B0 has a memoryarray, a row decoder (X-DEC), a column decoder (Y-DEC), a senseamplifier array (SA-ARY), and column switches (CSW) and global bit lines(GBL). The remaining memory banks B1-B3 are the same as the B0.

The memory control unit MCU and memory module MEM transact data witheach other through a 64-bit bus (MDQ). The 64-bit bus is divided foreight memories ME0-ME7 of the memory module so that each memory isconnected with an 8-bit bus. All memories ME0-ME7 operate simultaneouslyin response to the command from the memory control circuit MC, and thememory module MEM reads and writes 64-bits data at once. The memoriesME0-ME7 of this embodiment can be controlled separately among the fourmemory banks.

FIG. 3 and FIG. 4 show the detailed structure of the memory bank and theoperation of the memory module MEM. In the following explanation of thisembodiment, the memory is assumed to be a synchronous DRAM.

The signals on the signal lines shown in FIG. 1 will be explained on thetiming chart of FIG. 4. The CPU puts out the read command and memoryaddress, which are conducted via the arbiter circuit ARB over the ICOand IAD buses and put into the memory control circuit MC. The memorycontrol circuit puts out a bank activate command AC over a MC0 bus andputs out over a MAD bus a bank address BK0 (2 bits 13-12 of MAD) and rowaddress R0 (12 bits 11-0 of MAD) to the memory module. Subsequently, itputs out a read command RD over the MC0 bus and the bank address BK0(bits 13-12 of MAD) and column address CO (9 bits 8-0 of MAD) over theMAD bus. The commands and addresses released by the memory controlcircuit are put in parallel into the eight memories of the memory moduleMEM, and these memories have the same read operation. The transaction ofcommands, addresses and data is timed to the clock signal of the dataprocessing system in this embodiment.

The eight synchronous DRAMs (ME0-ME7) of the memory module MEM shown inFIG. 2 have common inputs of commands and addresses, and the operationof one synchronous DRAM (SDRAM0) will be explained in the following.

The bank activate command AC, bank address BK0 and row address R0 areput into the SDRAM0, and the row decoder X-DEC of bank B0 which isselected from among the four memory banks by the bank address BK0selects a word line WL out of 4096 word lines of the memory bank. Thememory bank B0 shown in FIG. 2 is shown in more detail in FIG. 3. Inresponse to the selection of a word line, data of memory cells of one4096-bit page is transferred over 4096 bit line pairs (BL0-0/BLB0-0through BL7-511/BLB7-511) to the sense amplifier array SA-ARY andamplified and held by 4096 amplifiers, respectively.

Subsequently, for reading out the data held by the sense amplifiers, theread command RD and the same bank address BK0 as for word line selectionand column address C0 are put into the SDRAM0 over the MC0 bus and MADbus, respectively. The bank address BK0 selects one of the four memorybanks in the same manner as word line selection, and the column decoderY-DEC of the selected bank selects eight column switches out of 4096column switches CSW by the column address CO. The eight column switchesselected by the column decoder Y-DEC lead out data from the senseamplifiers onto the global bit lines (GBL0-GBL7). The 8-bit data on theglobal bit lines is placed on the MDQ bus via the main amplifier MA andinput/output buffer IOBUF shown in FIG. 2. At the output of data ontothe MDQ bus, the remaining seven SDRAMS also release data, i.e., totaloutput of 64-bit data.

Subsequently, the memory control circuit MC puts out a precharge commandPRE and bank address BK0 for the precharge control. In consequence, theselection of word line of the selected memory bank is cancelled, andprecharging of the bit lines takes place. The timing of prechargingfollowing the column address output is probably stated in standards. Theprecharge timing is on expiration of 4 clocks following the columnaddress output in both cases of synchronous and asynchronous memories ofthis invention, although this is not compulsory.

Specifically, the RAS signal is brought to the high level to implementprecharging, and the page is closed. In the foregoing operation, thelatency of memory access after the memory control circuit MC puts outthe bank activate command AC to the memory module MEM until the memorymodule releases data is 7 cycles.

As the present embodiment employs an example of 4 bits burst mode asshown in FIG. 4, the access latency is 7 cycles. If one bit burst modeis employed, however, the access latency will be 3 cycles. One bit burstmode may be defined as a read out mode wherein one bit read out data isoutputted in response to one read command.

FIG. 5 shows the detailed arrangement of the memory control circuit MC.The memory control circuit includes a page access checking circuit PH, amode change circuit MODE, an address generation circuit ACG which issuesa control command and memory access address to the memory module, and aninput/output data control circuit DQB which controls the datatransaction with the memory module.

The page access checking circuit PH checks as to whether or not the rowaddress of the previous memory access and the row address of theimmediate memory access provided by the arbiter circuit ARB are equal.The mode change circuit MODE switches dynamically between the page-offmode for closing the page of memory following the access to the memorymodule and the page-on mode for retaining the page open.

The operation of the page access checking circuit PH and mode changecircuit MODE will be explained with reference to FIG. 6 and FIG. 7. FIG.6 shows the table held by the page access checking circuit PH, and itincludes fields of a row address select signal PS and comparison rowaddress TRAD for the four banks of the memory module MEM. The field ofrow address TRAD stores the row address of the previous access to eachmemory bank. The row address select signal PS at the high level or lowlevel indicates respectively that a row address TRAD of a bank isselected or not selected. The signal PS is low if the page is closed orhigh if the page is kept open at the end of previous access to a memorybank.

FIG. 7A shows the operational timing of the page access checking circuitPH. The memory control circuit MC receives a read command R and memoryaddress AD0 from the arbiter circuit ARB. The memory address AD0includes a bank address IAD(BANK) for specifying a bank and a rowaddress IAD(ROW) for specifying a word line, i.e., a page. The exampleshown in the figure is the case of a bank address IAD(BANK) of “1” and arow address IAD(ROW) of “38”.

The page access checking circuit PH makes reference to the table of FIG.6 to get comparison row address “5” for the bank address “1”, andcompares the input row address “38” with the comparison row address “5”.The input row address is not equal to the comparison row address.Namely, the immediate access and previous access to bank #1 differ inrow address, i.e., these accesses are to different pages. Consequently,a row address equality signal HT shown in FIG. 5 has a low level, and arow address inequality signal MSIG(1) for bank #1 is high, and it is putinto the mode change circuit MODE. The PSO signal is high which isderived from the value of PS for bank #1. Due to the result ofinequality of row address for bank #1, the comparison row address ofbank #1 is altered from “5”, to “38”.

Next, another case of operation shown in FIG. 7B will be explained. Thisis the case of a bank address IAD(BANK) of “3” and a row addressIAD(ROW) of “41” put into the memory control circuit MC.

The page access checking circuit PH makes reference to the table of FIG.6 to get comparison row address “41” for bank #3, and compares the inputrow address “41” with the comparison row address “41”. The input rowaddress is equal to the comparison row address. Namely, the immediateaccess and previous access to bank #3 are equal in row address, i.e.,these accesses are to the same page. Consequently, the row addressequality signal HT is high and the row address inequality signal MSIG(3)for bank #3 is low. The PSO signal is high which is derived from thevalue of PS for bank #3. Due to the result of equality of row addressfor bank #3, the comparison row address of bank #3 is retained to be“41”. The signal MSIG(*) (where * represents the bank number) is the rowaddress inequality signal for bank #*, and it becomes low for an eventof same page access or becomes high for an event of different pageaccess.

The mode change circuit MODE includes mode switch circuits (PRJ0-PRJ3)for switching the control mode of individual banks. The mode switchcircuit PRJ3 for bank #3 is made up of an access counter RC which countsthe number of times of successive events of access to different pagesand a switch circuit SW which switches the LPR(3) output signal betweenthe high and low levels depending on the count value of the accesscounter RC. A high-level LPR(3) signal indicates the page-off mode, anda low-level LPR(3) signal indicates the page-on mode. The remaining modeswitch circuits PRJ0-PRJ2, which are identical in arrangement to thePRJ3, switch the modes of bank #0 through bank #2. The page-on mode isto control the memory at an event of data read/write access to thememory module so that the page is kept open until the next access eventtakes place, and the page-off mode is to control the memory so that thepage is closed at each event of access to the memory module. TheRAS-down mode or page mode is equivalent to the page-on mode.

The access counter RC of the mode switch circuits PRJ0-PRJ3 can bepreset by the CPU of the number of times of successive events of accessto different pages. The CPU releases a counter preset command RSET anddata of the number of times of successive access events to differentpages. These preset command and data are delivered to the memory controlunit MCU over the CO0 and AD0 buses in FIG. 1, and put into the modeswitch circuits PRJ0-PRJ3 via the arbiter circuit ARB and preset to eachaccess counter RC. Although the CPU presets the number of times ofsuccessive access events to different pages in this embodiment, thisaffair is not compulsory, but it can be preset from the outside of thedata processing system or can be preset fixedly in the manufacturingprocess of the memory control unit.

FIG. 8 shows the operation of the mode switch circuits PRJ0-PRJ3. Thesecircuits PRJ0-PRJ3 control memory banks #0-#3 correspondingly. Thefollowing explains the operation of the mode switch circuit PRJ3 forbank #3 as representative of the circuits PRJ0-PRJ3. The mode switchcircuit PRJ3 is assumed to have preset value N of the number of times ofsuccessive access events to different pages in its access counter RC.The operation will be explained by being split into a first and secondparts.

In the first part of operation, the page-on mode is assumed to be setalready. A memory access request from the CPU is put into the memorycontrol circuit MC via the arbiter circuit ARB. The page access checkingcircuit PH checks whether the input access address is of the same pageas the previous access. The check result carried by the row addressinequality signal MSIG(3) is put into the mode switch circuit PRJ3. Thecircuit PRJ3 checks whether there have been N-time successive high-levelinputs, i.e., whether there have been successive access events todifferent pages equal in number to the value set in the access counterRC. If the number of high-level MSIG(3) inputs is less than N, thecircuit PRJ3 produces a low-level LPR(3) output to retain the page-onmode. Otherwise, if the number reaches N, the circuit PRJ3 produces ahigh-level LPR(3) output to make switching to the page-off mode andprecede to the second part of operation.

In the second part of operation, the mode switch circuit PRJ3 keeps thehigh-level LPR(3) output until a same page access arises, i.e., untilthe row address inequality signal MSIG(3) goes low, thereby retainingthe page-off mode. When the MSIG(3) signal goes low, i.e., at an eventof same page access, the circuit PRJ3 produces a low-level LPR(3) outputto make switching to the page-on mode and return to the first part ofoperation. The mode switch circuit PRJ3 for bank #3, and also theremaining circuits PRJ0-PRJ2 for banks #0-#2, repeat these first andsecond parts of operation in response to events of memory access.

FIG. 9 shows the operation of the address generation circuit ACG shownin FIG. 5, and FIG. 10 shows the signal waveforms at events of memoryaccess in each mode. As shown in FIG. 5, the address generation circuitACG receives the read command and memory address from the arbitercircuit ARB, a page access check signal HT and row address select signalPSO from the page access checking circuit PH, and an LPR signal from themode change circuit MODE.

The LPR signal is low in the page-on mode, or it is high in the page-offmode. In the page-on mode, the precharge command PRE is not issued atthe end of memory access, and the page is kept open. The followingexplains specifically the operation of cases (A) through (H) shown inFIG. 9.

(A) In case the row address select signal PS is high, the row addressequality signal HT is high and the LPR signal is low, indicating thatthe page is selected already and the immediate access is to the samepage, the memory control circuit puts out only the read command RD andcolumn address CO to the memory module MEM. This memory read access fordata transfer takes a latency of 5 cycles. This operation is shown bythe timing chart at the bottom in FIG. 10.

(B) In case the row address select signal PS is low, the HT signal ishigh and the LPR signal is low, indicating that the page is notselected, the memory control circuit puts out the bank activate commandAC and row address RO, and next the read command RD and column addressCO to the memory module. The read latency for data transfer is 7 cycles.This access operation taking place at a transition from the page-offmode to the page-on mode is shown by the second timing chart from thebottom in FIG. 10.

(C) In case the row address select signal PS is high, the HT signal islow and the LPR signal is low, indicating an access event to a differentpage, the memory control circuit puts out the precharge command PRE,bank activate command AC and row address RO, and next the read commandRD and column address CO to the memory module. The read latency for datatransfer is 9 cycles. This access operation directed to a different pagein the page-on mode is shown by the timing chart at the top in FIG. 10.

(D) In case the row address select signal PS is low, the HT signal islow and the LPR signal is low, indicating that the page is not selected,the memory control circuit puts out the bank activate command AC, andnext the read command RD to the memory module. The read latency for datatransfer is 7 cycles.

These operations (A)-(D) are of the page-on mode, and the followingoperations (E)-(H) are of the page-off mode. In the page-off mode, theprecharge command PRE is issued at the end of memory access, and thememory module MEM has its page closed, i.e., the unselected state ofword line is restored.

(E) In case the row address select signal PS is high, the HT signal ishigh and the LPR signal is high, indicating that the page is selectedalready and the immediate access is to the same page, the memory controlcircuit puts out the read command RD, column address and prechargecommand PRE to the memory module, and closes the page following the dataoutput. The read latency for data transfer is 5 cycles.

(F) In case the row address select signal PS is low, the HT signal ishigh and the LPR signal is high, indicating that the page is notselected, the memory control circuit puts out the bank activate commandAC and row address, the read command RD and column address, and theprecharge command PRE sequentially to the memory module. The readlatency for data transfer is 7 cycles.

(G) In case the row address select signal PS is high, the HT signal islow and the LPR signal is high, indicating that a page is selectedalready, but the immediate access is to a different page, the memorycontrol circuit puts out the precharge command PRE, bank activatecommand AC and row address, the read command RD and column address, andthe precharge command PRE sequentially to the memory module. The readlatency for data transfer is 9 cycles. This access operation takingplace at a transition from the page-on mode to the page-off mode isshown by the second timing chart from the top in FIG. 10.

(H) In case the row address select signal PS is low, the HT signal islow and the LPR signal is high, indicating that the page is notselected, the memory control circuit puts out the bank activate commandAC and row address, the read command RD and column address, and theprecharge command PRE sequentially to the memory module. The readlatency for data transfer is 7 cycles. This access operation takingplace in the succession of the page-off mode is shown by the thirdtiming chart from the top in FIG. 10.

The values of write latency shown at the bottom of table in FIG. 9 areexamples of the operation of the address generation circuit ACG at theinput of a write command WT. At data writing to the memory module, theread command RD in the command sequence is replaced with the writecommand WT.

At an event of access to a different page in the page-on mode, theimmediate page needs to be closed, i.e., it is done by making theselected word line unselected and issuing the precharge command PRE forprecharging the data lines. In this case, the closed page must be openedagain, and therefore the read latency becomes 9 cycles.

At successive access events to different pages, the page-on mode isswitched to the page-off mode. At an access event to a different page inthe page-off mode, the page is already closed in the previous access andthe issuance of precharge command PRE at the beginning is not needed,resulting in a latency of 7 cycles.

At a transition from the page-on mode to the page-off mode, there is nonecessity of having the continuation of different page access, and it ispossible to have switching to the page-on mode at a single event ofaccess to a different page in the page-on mode. This can be done bypresetting the access counter RC to “1”. It is also possible to makeswitching from the page-on mode to the page-off mode depending on theproportion of frequencies of same page access and different page access,instead of being responsive to successive access events to differentpages. Further, in case of the page-on mode, it can be switched forcedlyto the page-off mode by carrying out the procedure as shown in FIG.9(E).

At an event of access to the same page in the page-off mode, thepage-off mode is switched to the page-on mode. An access event to a samepage in the page-on mode is to the page which is open currently, insteadof needing another page to open, and the latency becomes 5 cycles. Inthis case also, the page-off mode can be switched forcedly to thepage-on mode by carrying out the procedure as shown in FIG. 9(D). Thismeans may be designed to make switching to the page-on mode followingseveral times of page access events in the page-off mode, i.e.,following the continuation of the state of (E) in FIG. 9. It is possibleto provide a register similar to the access counter RC for setting thenumber of times of page access before switching to the page-on mode.

As described above, the present invention is designed to switch betweenthe page-on mode and the page-off mode dynamically in response toindividual access events, thereby enabling high-speed data transferbetween the CPU and the memory module.

FIG. 11 shows the signal waveforms of operation when a refresh commandis put into the memory control circuit MC. At the input of the refreshcommand, a precharge-all command PAL is issued to precharge all memorybanks of the memory module, and thereafter a refresh command REF isissued. After all memory banks are precharged by the precharge-allcommand PAL, all row address select signals PS in the page accesschecking circuit PH are turned low.

FIG. 12A shows a typical example of access from the CPU to the memorymodule MEM. There is a case of successive access events to a same pageand successive access events to different pages occurring alternately.Periods T1 and T3 are of successive access events to a same page andperiods T2 and T4 are of successive access events to different pages.

FIG. 12B compares the latencies among the operation fixed to the page-onmode, the operation fixed to the page-off mode, and the inventive modeswitching operation in the periods T1 and T3 of successive access eventsto the same page. FIG. 12C compares the latencies among the operationfixed to the page-on mode, the operation fixed to the page-off mode, andthe inventive mode switching operation in the periods T2 and T4 ofsuccessive access events to different pages. FIGS. 12B and 12C revealthat, according to this invention, the system operates in the page-onmode during the periods T1 and T3 of successive access events to thesame page and operates by switching to the page-off mode during theperiods T2 and T4 of successive access events to different pages.

Based on this mode switching, it becomes possible constantly to minimizethe latency and make high-speed access to the memory module.Furthermore, it becomes possible to reduce the power consumption of thememories owing to the smaller number of times of operation of the senseamplifiers of the memories.

In the foregoing first embodiment, the memory module has a number ofbanks. However, the present invention is essentially capable of beingapplied to data processing systems in which memory modules do not havememory banks, and is capable of accomplishing high-speed access to thememories of these systems.

FIG. 13 shows by block diagram the memory control circuit based on thesecond embodiment of this invention, with the names and symbols of itemscommon to the first embodiment being used. Other constituents of dataprocessing system which are identical to the first embodiment are notshown and explained repeatedly.

This memory control circuit MC1 includes a predicted address generationcircuit PFS which issues the next address (the previous address added bya certain offset value) in advance based on the address provided by thearbiter circuit ARB. The memory control circuit further includes a modechange circuit MODE0 which checks as to whether or not the immediateaccess address is of the same page as the previous access thereby toswitch dynamically between the page-off mode for closing the page of thememory module or the page-on mode for opening the page.

It further includes a page access checking circuit PH0 which checkswhether or not the row address of the immediate access is equal to therow address of the previous access. It further includes a predictedaddress checking circuit PH1 which checks as to whether or not the rowaddress that has been issued in advance by the predicted addressgeneration circuit PFS is equal to the row address provided by thearbiter circuit ARB, and a predicted address generation mode changecircuit MODE1 which validates or invalidates dynamically the predictedaddress generation in response to the result provided by the predictedaddress checking circuit PH1. It further includes an input/output datacontrol circuit DQB which controls the data transaction with the memorymodule and an address generation circuit ACG which produces a controlcommand and address for the memory module. The mode change circuit MODE0and predicted address generation mode change circuit MODE1 operate inthe same manner as the mode change circuit MODE of FIG. 5.

The operation of the predicted address generation circuit PFS andpredicted address checking circuit PH1 will be explained.

FIG. 14 shows a table which belongs to the predicted address checkingcircuit PH1, in which are contained row addresses of individual banks ofthe memory module. Each row address is the comparison row address PRADwhich has been issued by the predicted address generation circuit PFSbefore the immediate memory access.

FIG. 15 shows a table which belongs to the predicted address generationcircuit PFS, in which are contained the valid signals PF for individualbanks indicative of as to whether the predicted address to be put intothe page access checking circuit PH0 is validated or invalidated. A highvalid signal PF indicates valid, and a low PF signal indicates invalid.

FIGS. 16A and 16B show an example of operation of the predicted addressgeneration circuit PFS and predicted address checking circuit PH1. InFIG. 16A, the read command R, a bank address IAD(BANK) having value “2”,and a row address IAD(ROW) having a value “105” are sent to the memorycontrol circuit MC1 over the IC0 and the IAD buses. The predictedaddress generation circuit PFS responds to this address input to releasea bank address SAD(BANK) having value “2” and a row address SAD(ROW)having value “105” to the predicted address checking circuit PH1 overthe SAD bus.

The predicted address checking circuit PH1 compares the input rowaddress value “105” with the comparison row address PRAD having value“105” of bank #2 in the table of FIG. 14. A result of equality of thiscase, indicative of same page access, produces a high-level HSIG(2)signal, and the value of PRAD of bank #2 is kept unchanged at “105”.

Subsequently, the predicted address generation circuit PFS puts out apredicted bank address SAD(BANK) having value “3” and row addressSAD(ROW) having value “105” to the predicted address checking circuitPH1 over the SAD bus. It also puts out a low PFE signal to the pageaccess checking circuit PH0.

The predicted address checking circuit PH1 revises the value “15” ofcomparison row address PRAD of bank #3 to the value “105” of inputpredicted row address SAD(ROW) in the table of FIG. 14. Since thepredicted bank address SAD(BANK) provided by the predicted addressgeneration circuit PFS over the SAD bus has value “3”, the valid signalPF for bank #3 in the table of FIG. 15 is read out. This valid signal PFis high, causing the predicted address to be validated, and the PFEsignal is turned low.

The LPF(0-3) signal released by the predicted address generation modechange circuit MODE1 to the predicted address generation circuit PFS iscorrespondent to individual memory banks, and this signal is used to setthe valid signal PF to high or low. A high LPF signal bit signifies thevalidation of predicted address, and a low LPF signal bit signifies theinvalidation of the predicted address. With LPF(2) being high, the validsignal PF has its bit for bank #2 set to high.

In FIG. 16B, the read command R, a bank address IAD(BANK) having value“0” and a row address IAD(ROW) having a value “18” are put into thememory control circuit MC1 over the IC0 and IAD buses. The predictedaddress generation circuit PFS responds to this address input to releasea bank address SAD(BANK) having value “0” and a row address SAD(ROW)having value “18” to the predicted address checking circuit PH1 over theSAD bus.

The predicted address checking circuit PH1 compares the input rowaddress value “18” with the comparison row address PRAD with value “8”of bank #0 in the table of FIG. 14. A result of inequality of this case,produces a low-level HSIG(0) signal, and the value of comparison rowaddress PRAD of bank #0 is kept unchanged at “8”.

Subsequently, the predicted address generation circuit PFS puts out apredicted bank address SAD(BANK) having value “1” and a row addressSAD(ROW) having value “18” to the predicted address checking circuitPH1. It also puts out a low PF1 signal to the predicted address checkingcircuit PH1.

The predicted address checking circuit PH1 revises the value “6” ofcomparison row address PRAD of bank #1 to the value “18” of predictedrow address SAD(ROW) in the table of FIG. 14. Since the predicted bankaddress SAD(BANK) provided by the predicted address generation circuitPFS over the SAD bus has value “1”, the valid signal PF for bank #1 isread out. This valid signal PF is low, causing the predicted address tobe invalidated, and the PFE signal is turned high. The low LPF(1) signalcauses the valid signal PF1 for bank #1 of the valid signal PF to be setto low.

FIG. 17 shows the operation of the predicted address generation modechange circuit MODE1. The circuit MODE1 is identical in arrangement andoperation to the mode change circuit MODE shown in FIG. 2. The operationwill be explained by being split into a first and second parts.

The circuit MODE1 responds to each input of memory address from thearbiter circuit ARB to check as to whether there have been M-timesuccessive outputs of high-level HSIG signal. If there have not beenM-time successive outputs of high HSIG signal, the LPF signal is madelow to retain the predicted address invalid mode. If there have beenM-time successive outputs of high-level HSIG signal, the LPF signal isturned high to make switching to the predicted address valid mode andprecede to the second part of operation.

In the second part of operation, the circuit MODE1 keeps the predictedaddress valid mode and the high LPF signal until the HSIG signal turnslow. When the HSIG signal turns low, the LPF signal is turned low tomake switching to the predicted address invalid mode and return to thefirst part of operation. This control operation is repeated.

FIGS. 18A and 18B show the operation of the page access checking circuitPH0 and address generation circuit ACG. In FIG. 18A, the read command Rand address A0 are sent to the memory control circuit MC1 over the IC0bus and IAD bus, respectively. The predicted address generation circuitPFS responds to this address input to send the address A0 and predictedaddress A1 to the page access checking circuit PH0 over the SAD bus. Thepage access checking circuit PH0 recognizes the address A0 to be of samepage access, producing a high HT signal, low MSIG signal and high PS0signal. The predicted address A1 is recognized to be valid by the lowPFE signal, and it is to be checked as for page access by the pageaccess checking circuit PH0. Consequently, it is recognized to be ofdifferent page access, resulting in a low HT signal and high PS0 signal.

The address generation circuit ACG receives the read command for theaddress A0 from the page access checking circuit PH0 and the HT, PS0 andPFE signals from the predicted address generation circuit PFS, and itsends the read command RD, bank address B0 and column address C0 for theaddress A0 to the memory module. For the predicted address A1, it sendsthe precharge command PRE, bank activate command AC, bank address B1 androw address R1 to the memory module.

In FIG. 18B, in response to the input of the read command R over the IC0bus and address A0 over the IAD bus to the memory control circuit MC1,the predicted address generation circuit PFS sends the address A0 andpredicted address A1 to the page access checking circuit PH0 over theSAD bus. The page access checking circuit PH0 recognizes the address A0to be of different page access, producing a low HT signal, high MSIGsignal and low PS0 signal. The predicted address A1 is recognized to beinvalid by the high PFE signal, and it is not to be checked as for pageaccess by the page access checking circuit PH0.

The address generation circuit ACG receives the read command for theaddress A0 from the page access checking circuit PH0 and the HT, PS0 andPFE signals from the predicted address generation circuit PFS, and itsends the bank activate command AC, read command RD, bank address B0,row address R0, and column address C0 for the address A0 to the memorymodule. For the predicted address A1, it sends nothing.

FIG. 19 explains the overall operation of the memory control circuitMC1. The read command R0 and address A0 are put into the predictedaddress generation circuit PFS over the IC0 bus and IAD bus,respectively. The predicted address generation circuit PFS first issuesthe address A0 and next issues the predicted address A1 over the SADbus. The predicted address A1 is of a bank different from that of theaddress A0. The address A0 is put into the page access checking circuitPH0.

If the circuit PH0 recognizes the input row address to be equal to thecomparison row address, i.e., both addresses are of the same page, itproduces a high HT signal as in the case of the first embodiment. Theaddress generation circuit ACG sends the read command RD, bank addressB0 and column address C0 to the memory module. The predicted address A1is put into the page access checking circuit PH0 after the address A0.The page access checking circuit PH0 recognizes the input row address tobe different from the comparison address, causing the HT signal to turnlow, and the address generation circuit ACG produces the prechargecommand PRE thereby to hold the data of the predicted address in theDRAM sense amplifier and puts out the bank activate command AC, bankaddress B1 and row address R1.

Subsequently, when the record command R1 and address A1 are put into thepredicted address generation circuit PFS over the IC0 and IAD,respectively, the circuit PFS first issues the address A1 and nextissues the predicted address A2 over the SAD bus. Since the row addressfor the address A1 has been selected by the previous address A0, the HTsignal is high and the intended data is delivered to the memory moduleat a minimal latency of 2 cycles. Based on the advanced issuance of thenext address in this manner, the access frequency to the same pageincreases, and the access to the memory module can be sped up.

FIG. 20 shows by block diagram the memory control circuit based on thethird embodiment of this invention. This circuit MC2 is derived from thememory control circuit MC of the first embodiment, with an automaticaddress alignment circuit AT being added thereto.

FIG. 21 shows by block diagram the data processing system which includesthe memory control circuit MC2. The data processing system is made up ofa memory module MEM, a data processor MS2 having a CPU which makesaccess to the memory module and primary cache L1C, a PCI bridge circuitBRG, and a memory control circuit MCU2 which controls the memory moduleMEM.

The memory module MEM is derived from the one shown in FIG. 1 with theaddition of a module status register MREG for holding module statusinformation including the bank address, row address and column addressindicative of the structure of memory module. The data processor MS2 isderived from the one shown in FIG. 1 as MS0 with the addition of a cachestatus register LREG for holding cache status information including thetag, index and line size indicative of the structure of primary cache.

The operation for transferring the cache status information held by thecache status register LREG and module status information held by themodule status register MREG to the automatic address alignment circuitAT will be explained in connection with FIG. 20 and FIG. 21.

The cache status information is transferred from the cache statusregister LREG to the automatic address alignment circuit AT as follows.The CPU sends over the CO0 and IC0 buses a command WC of transferringthe cache status information held by the cache status register LREG tothe memory control circuit, and sends the cache status information tothe automatic address alignment circuit AT in the memory control circuitover the DQO and IDQ buses. The number of bits of line is sent over theIDQ(4-0) lines, the number of bits of index is sent over the IDQ(9-5)lines, and the number of bits of tag is sent over the IDQ(14-10) linesto the automatic address alignment circuit AT. By the transfer commandWC, the cache status information is put into the register CREG in theautomatic address alignment circuit AT.

Subsequently, the CPU sends over the CO0 and IC0 buses a command oftransferring the module status information held by the module statusregister MREG to the memory control circuit. The address generationcircuit ACG in the memory control circuit sends a command of reading themodule status information out of the module status register MREG to thememory module. Consequently, the module status information is sent fromthe memory module to the register in the automatic address alignmentcircuit over the MDQ and IDQ buses.

FIG. 22 shows an example of operation of the automatic address alignmentcircuit AT of the case of the primary cache L1C with a line size of 5bits, an index size of 8 bits and a tag size of 19 bits, and of thememory module MEM with a column address of 9 bits, a bank address of 2bits and a row address of 12 bits. The IAD(31-0) is the address which isput into the automatic address alignment circuit AT, and SAD(22-0) isthe address which is released by being treated by the automatic addressalignment circuit AT.

Indicated by LIN0-LIN4 are 5-bit lines, IND0-IND7 are an 8-bit index,and TAG0-TAG18 are a 19-bit tag. C0-C8 are a 9-bit column address, B0-B1are a 2-bit bank address, and R0-R11 are a 12-bit row address. The 5-bitlines, 8-bit index and 19-bit tag are first assigned sequentially fromthe lowest bit of IAD(31-0), and next the 9-bit column address, 2-bitbank address and 12-bit row address are assigned sequentially from thelowest bit of SAD(22-0). Subsequently, the bank address is assigned fromthe lowest bit of tag.

FIG. 23 shows another example of operation of the automatic addressalignment circuit AT of the case of the primary cache L1C with a linesize of 5 bits, an index size of 9 bits and a tag size of 18 bits, andof the memory module MEM with a column address of 9 bits, a bank addressof 2 bits and a row address of 12 bits. The IAD(31-0) is an addresswhich is put into the automatic address alignment circuit AT, andSAD(22-0) is an address which is released by being treated by theautomatic address alignment circuit AT.

Indicated by LIN0-LIN4 are 5-bit lines, IND0-IND8 are a 9-bit index, andTAG0-TAG17 are a 18-bit tag. C0-C8 are a 9-bit column address, B0-B1 area 2-bit bank address, and R0-R11 are a 12-bit row address. The 5-bitlines, 9-bit index and 18-bit tag are assigned first sequentially fromthe lowest bit of IAD(31-0), and next the 9-bit column address, 2-bitbank address and 12-bit row address are assigned sequentially from thelowest bit of SAD(22-0). Subsequently, the bank address is assigned fromthe lowest bit of tag.

Based on the automatic assignment of the bank address to the tag bits sothat the read operation for replacing the cache entry caused by theerror of primary cache and the write operation for write-back take placein different banks, thereby lowering the frequency of operation ofdifferent pages in the same bank, it becomes possible to speed up theoperation of the DRAM and synchronous DRAM.

FIG. 24 shows a set of timing charts showing the operation of the fourthembodiment of this invention, in which the memory module of FIG. 1 isformed of a DDR (double data rate) synchronous DRAM. The DDR-SDRAM hasmultiple memory banks and associated sense amplifiers as in the case ofthe SDRAM. The DDR-SDRAM features the data transfer at the rising andfalling edges of the clock signal. The arrangement of this embodiment isvirtually identical to the first embodiment, and its explanation andillustration will be omitted. This embodiment enables the high-speedoperation of the DDR-SDRAM.

Shown in FIG. 24 are read latencies of the operational waveforms of thecommands and addresses put out by the memory control circuit MC to thememory module MEM and data read out of the memory module in response tothe input of the read command R to the memory control circuit MC invarious modes switched by the memory control circuit MC.

At an event of different page access in the page-on mode, the prechargecommand PRE is issued to close the page which is open currently and nextanother page is opened, resulting in a read latency of 8 cycles. Atsuccessive events of different page access, the page-on mode is switchedto the page-off mode. The issuance of precharge command PRE at thebeginning is not needed, since the page has been closed in the previousaccess, resulting in a read latency of 6 cycles. At an event of samepage access in the page-off mode, the mode is switched to the page-onmode. The same page access in the page-on mode is to the page which isopen, instead of having to open another page, resulting in a latency of4 cycles. Based on the mode switching control for the memory module ofDDR-SDRAM, the memory module access can be sped up.

FIG. 25 shows the operation of the mode change circuit based on thefourth embodiment. This mode change circuit has the same arrangement asthe mode change circuits (PRJ0-PRJ3) of the first embodiment shown inFIG. 5, with common symbols being used in both figures. The followingexplains the mode change circuit PRJ3 which controls bank #3 out of fourbanks of the DDR-SDRAM. The mode switch circuit PRJ3 is assumed to havepreset value N of the number of times of consecutive access events todifferent pages in its access counter RC. The operation will beexplained by being split into three parts.

In the first part of operation, the page-on mode is assumed to be setalready. A memory module access request from the CPU is put into thememory control circuit MC via the arbiter circuit ARB. The page accesschecking circuit PH checks whether the input access address is of thesame page. The check result carried by a row address inequality signalMSIG(3) is put into the mode switch circuit PRJ3. The circuit PRJ3checks whether there have been N-time successive high-level inputs,i.e., whether there have been successive events of different page accessequal in number to the value set in the access counter RC. If the numberof high-level MSIG(3) inputs is less than N, the circuit PRJ3 produces alow-level LPR(3) output to retain the page-on mode. If the number ofsuccessive high-level MSIG(3) inputs reaches N, the circuit PRJ3produces a high-level LPR(3) output to switch to the page-off mode, andprecedes to the second part of operation.

In the second part of operation, the mode switch circuit PRJ3 in thestate of page-off mode checks whether the MSIG(3) signal is high. If therow address inequality signal MSIG(3) is low, i.e., if it is same pageaccess, the circuit PRJ3 increments the value N of the access counter RCby one, turns the LPR(3) output to the low level, and returns to thefirst part of operation. If the MSIG(3) signal is high, indicative ofdifferent page access, the circuit PRJ3 decrements the value N of theaccess counter RC by one and keeps the LPR(3) output high to retain thepage-off mode.

In the third part of operation, the LPR(3) output is kept high until asame page access arises after the page-off mode has been retained in thesecond part of operation, i.e., until the row address inequality signalMSIG(3) goes low, thereby retaining the page-off mode. When the MSIG(3)signal turns low, i.e., it becomes same page access, the circuit PRJ3turns the MSIG(3) output to the low level to switch to the page-on mode,and returns to the first part of operation.

The second part of operation enables sophisticated mode switching, andthe further speed-up of the data processing system is made possible. Theprinciple of the second embodiment can be applied to other embodiments,inclusive of its application to the operation shown in FIG. 17.

FIG. 26 shows a set of timing charts showing the operation of the fifthembodiment of this invention, in which the memory module of FIG. 1 isformed of an EDO (extended data output) DRAM. The EDO-DRAM also hassense amplifiers corresponding to the memory banks. The EDO-DRAMfeatures the asynchronous data transfer. By applying the presentinvention to the memory module MEM formed of the EDO-DRAM, a dataprocessing system capable of high-speed operation can be accomplished.

Shown in FIG. 26 are the operational waveforms of the commands andaddresses put out by the memory control circuit to the memory module MEMand data read out of the memory module in response to the input of theread command R to the memory control circuit MC in various modesswitched by the memory control circuit MC.

In the case of the EDO-DRAM, the page is closed when the RAS signal goeshigh while the CAS signal is high. When the RAS signal goes low, withthe CAS signal being high, the page specified by the row address opens.When the CAS signal goes low while the RAS signal is low, data specifiedby the column address is put out. The CAS and RAS signals are low-activesignals, although the bar or slash symbol is not put on these signalnames throughout this document.

At an event of different page access in the page-on mode, the RAS signalis turned high temporarily to implement the precharging in order toclose the page which is open currently. The RAS signal is turned lowthereafter to open the page specified by the row address R0.Subsequently, the CAS signal is turned low four times to put out dataspecified by the column addresses C0, C1, C2 and C3. The read latency is8 cycles. At successive events of different page access, the page-onmode is switched to the page-off mode. Since the page has been closed inthe previous access in the case of different page access, it is notnecessary to turn the RAS signal high at the beginning to close thepage, and the latency is 6 cycles.

At an event of same page access in the page-off mode, the mode isswitched to the page-on mode. The same page access in the page-on modeis to the page which is open currently, instead of having to openanother page, resulting in a latency of 4 cycles. Based on the modeswitching control for the memory module of EDO-DRAM, a high-speed dataprocessing system can be accomplished. It should be noted thatconstituents other than the EDO-DRAM, i.e., CPU, memory control unitMCU, etc., in FIG. 25 operate in synchronism with the clock signal CLKin issuing commands and addresses, and therefore the clock signal CLK isshown.

Although term “access” has been used in the explanation of the firstthrough fifth embodiments, it signifies here the operation of putting anaddress into a memory and reading out data from the memory. Anoperational mode is established by setting a certain value in theregister. In the foregoing embodiments, the mode is set by the registerwhich is included in the CPU or memory controller.

It is possible for the foregoing embodiments to have a register forsetting the modes of allowing and not allowing the switching between thepage-on mode and page-off mode.

The data processor and memory control unit, i.e., memory controller, maybe formed on separate semiconductor chips, or they may be formed on onesemiconductor chip. A data processor and memory controller formed on onesemiconductor chip can have the data bus DQO of a larger number of bitsthan the formation on different semiconductor chips, and moreover theirshorter distance enables much faster data transfer.

It is also possible to put a memory controller, which has been designedin the past or designed by a third party, on the same semiconductor chipas of the data processor thereby to complete a one-chip data processor.In this case, it is possible to record design data of the memorycontroller on a recording medium and offer to the designer of dataprocessor.

It is also possible to combine a data processor provided by a thirdparty with the inventive memory controller, and supply the finishedsemiconductor device to the third party. The memory control unit may beincluded in the memory module. Forming the memory controller in the dataprocessor or memory module reduces the work load of the manufacturer ofdata processing system and also enhances the compactness of dataprocessing system.

It is also possible to form part or whole of the memory module on thesame semiconductor chip as of the data processor in the course ofprogress of the manufacturing process of semiconductor devices, therebyaccomplishing a more compact one-chip data processing system.

It is also possible to use the CPU to perform the memory control circuiton a software basis. This is possible obviously even in case the memorymodule and data processor are not formed on the same semiconductor chip.This scheme, however, will compel the CPU to work harder for thetreatment of address and sacrifice the speed of other process inexchange for a reduced hardware component parts.

Based on a separate arrangement of this invention, the effectiveness ofthis invention can be attained without an excessive addition to the CPU.A one-chip data processor IC-DPD and a one-chip memories (IC-ME1 throughIC-ME4) may be packaged in a module to complete a semiconductor deviceas shown in FIG. 27. This arrangement is known to be a multi-chip moduleor multi-chip package.

Although the embodiments of the high-speed data processing system havebeen explained, the present invention is not confined to theseembodiments, but various other embodiments are possible withoutdeparting from the essence of the present invention.

For example, it is possible to combine the predicted address generationcircuit and predicted address checking circuit of the second embodiment,the automatic address alignment circuit of the third embodiment, and therevision of value of the access counter shown in the fourth embodimentwith other embodiments. Combining the predicted address generationcircuit and predicted address checking circuit with other embodimentsenables the enhancement of the frequency of access to a same page, andfurther speed-up of data processor can be accomplished. Combining theautomatic address alignment circuit with other embodiments enables thereduction of the frequency of operation of different pages, and furtherspeed-up of data processor can be accomplished. Combining the revisionof value of the access counter with other embodiments enables moresophisticated mode switching, and further speed-up of data processor canbe accomplished. It is obviously possible to apply the above-mentionedcombinations to other embodiments so as to bring out theirmultiplicative effectiveness.

Although the memory modules of the first, third, fourth and fifthembodiments are each made up of multiple memory banks, the presentinvention is also applicable to data processing systems having memorymodules without a bank structure. It is also possible to speed up thememory access of data processing systems having memory modules without abank structure.

According to the present invention, as described above, the provision ofautomatic mode change control which is responsive to the type of memoryaccess enables the reduction of the latency of access to the memorymodule, whereby a high-speed data processing system can be accomplished.Furthermore, based on the switching control of next address generationor the automatic address alignment, a high-speed data processing systemcan be accomplished.

What is claimed is:
 1. A semiconductor device comprising: a memorycontroller receiving commands from a CPU, and controlling a memory,wherein said memory controller has a first mode and a second mode,wherein said memory comprises a plurality of word lines, data lines, andmemory cells, wherein said memory is controlled to precharge after aread access in said first mode, wherein said memory is controlled toreceive a next access command without a precharge operation after a readaccess in said second mode, wherein said memory controller has a circuitcomparing one address inputted and the address previous to said oneaddress to control the mode for access commands corresponding toaddresses inputted after said one address, wherein after a first numberof successive times a different word line is selected, said memorycontroller changes said second mode to said first mode, and wherein saidcircuit controls sad first number.
 2. The semiconductor device accordingto claim 1, wherein said memory is an SDRAM.
 3. The semiconductor deviceaccording to claim 1, wherein during said first mode, if an access to asame word line continues, a precharge operation before a read operationis abridged, and wherein during said second mode, if an access to adifferent word line occurs, a precharge operation is performed before aread operation.
 4. The semiconductor device according to claim 1,further comprising: a DRAM memory to be controlled by said memorycontroller, wherein said DRAM memory is molded in the same package asthe memory controller.
 5. A semiconductor device comprising: a memorycontroller receiving commands from a CPU, and controlling a memory,wherein said memory controller has a first mode and a second mode,wherein said memory comprises a plurality of word lines, data lines, andmemory cells, wherein said memory is controlled to perform a prechargeoperation after a read access in said first mode, wherein said memory iscontrolled to receive a next access command without a prechargeoperation after a read access in said second mode, wherein said memorycontroller has a circuit comparing one address inputted and the addressprevious to said one address to control the mode for access commandscorresponding to addresses inputted after said one address, and whereinin said first mode if a same word line is selected successively, saidmemory controller changes the mode to said second mode for a next accesscommand.
 6. The semiconductor device according to claim 5, wherein insaid first mode if a different word line is selected successively, saidmemory controller keeps the mode to said first mode for a next accesscommand.
 7. The semiconductor device according to claim 6, wherein insaid second mode if a different word line is selected for a first numberof successive times, said memory controller changes said second mode tosaid first mode, and wherein said circuit controls said first number. 8.The semiconductor device according to claim 6, wherein said memory is anSDRAM.
 9. The semiconductor device according to claim 7, furthercomprising: a DRAM memory to be controlled by said memory controller,wherein said DRAM memory is molded in the same package as the memorycontroller.